The present invention is directed to digital projectors incorporating light engines with color splitting-converging prisms, and more particularly to an adjustable convergence mechanism for adjusting the position of Digital Micromirror Device (DMD) sub-assemblies of a digital projector.
A typical color digital projector consists of a lamp, an illumination system, and a color splitting-recombining light engine. The optical function of a light engine is to split uniform illumination light into Red/Green/Blue (RGB) channels, merging the three channels onto an imaging device or optical panel such as an LCD (Liquid Crystal Display) or DMD (Digital Micromirror Device), and then re-combining all three channels into a single illumination light beam that is projected on a screen via a projection lens.
The DMD is an electromechanical device consisting of millions of microscopic mirrors that modulates light by independently flipping each mirror through a +−12 degree angle. The design of the DMD requires creation of a light cone with an f/#2.4-2.5 for maximum light throughput in the projector. Using three such DMDs on a prism (e.g. Phillips® prism, plumbicon, etc.), a white light cone of f/2.4 can be separated into red, green, and blue. Each color is individually modulated by the DMD and then recombined by the prism.
The positions of red, green and blue DMDs are critical for correct colour convergence of the output image. For an optimal image, the same pixels from each of the red, green and blue DMDs must be 100% overlapped. In normal usage environments, convergence may drift (in the order of micrometers) as a result of environmental changes, vibration, etc., which can create unacceptable color separation. However, the light engines used in conventional projectors are located deep inside the projector and therefore hard to access, making convergence correction a difficult and time-consuming operation for service personnel in the field.
Accordingly, it is an objective of the present invention to provide a mechanism for convergence adjustment without requiring access to the light engine.